Hypercoordinate organosilicon compounds

Fig. 16. Observed Si--N bond lengths in hypercoordinate organosilicon compounds (Cambridge Structural Database, Version 5.10) and density functional theory (DFT) calculations of energy differences. 4En based on the experimental structural data and correlated potential for the simplest model complex HjN- -SiHj...

For bis[2,6-bis(dimethylaminoethyl)phenylsilane, the second selected hypercoordinate organosilicon compound, its structure determination proves a formally eight-coordinate silicon center with averaged intramolecular distances of 289 and 310 pm for the two different N Si interactions in the differently overcrowded donor-acceptor complex halves (Fig. 4a). They vary by 21 pm in length and their bond enthalpies have to be each separately approximated, analogously to the ones in the seven-coordinate compound (Figs. 3 and 4). Altogether four rotations around the... 

Yamaguchi S, Akiyama S, Tamao K. Photophysical properties changes caused by hypercoordination of organosilicon compounds from trianthrylfluorosilane to trianthryldif-luorosilicate. J Am Chem Soc 2000 122 6793-4. 

The first observation of penta- and hexaeoordinate silicon compounds was reported at the beginning of the 19th century by Gay-Lussac [87] and Davy [88], Subsequent investigation of hypercoordination in silicon compounds stimulated widespread use of nucleophilic activation and catalysis in the application of organosilicon compounds as reactive species in organic synthesis. Synthetic application for silicon-fluorine bond formation can be found in several reviews over the last two decades, and this section focuses on recent advances in the use of hypervalent organosilicon compounds in selective organic synthesis, in particular, selective carbon-carbon bond formation [89]. 

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